1. Field of the Invention
The present invention relates to an optical film composite, and in particular, to an optical film composite applicable in a direct type back light module, especially a direct type LED back light module.
2. Description of the Prior Art
Liquid crystal displays (LCDs) have advantages of high image quality, low radiation, low power consumption, and good space utilization, and thus gradually replace the existing cathode-ray tube (CRT) display and become popular in the market. The main structure of the LCD includes two parts, that is, a liquid crystal panel and a back light module. As the liquid crystal panel does not emit light, the back light module is required to provide a light source needed for displaying images by the LCD, to enable the LCD to display images normally.
One of commonly used light sources of the back light module is a cold cathode fluorescent lamp (CCFL). In a direct type back light module, the lamps are disposed in parallel under the liquid crystal panel, and if the light is not suitably diffused and uniformized suitably, obvious lamp contour is easily caused on the display screen due to non-uniform distribution of light intensity, and thus the imaging quality is reduced. Furthermore, the higher the demand on brightness is, or the larger the size of the display is, the higher the number of the lamps that are needed is, and the more serious the emerged mura phenomenon is. Therefore, it becomes a major bottleneck in development in the field of LCD.
Another light source applicable in the back light module is a light emitting diode (LED). Due to the advantages of low power consumption, high brightness, and no pollution of LEDs, the back light module using LEDs as the light source has become one of the important research and development directions at present. However, as the LEDs are point light source and have high directionality, hot spot effect easily occurs. Therefore, if the light of the back light module using LEDs as the light source is not diffused and uniformized suitably, the mura phenomenon easily occurs. One solution for this problem is to increase the number of the LEDs to reduce the pitch among the LEDs. However, by this manner, the number of the LEDs is significantly increased, such that the overall cost is increased, and excessively heat is generated, and thus the service life and quality of other components are impacted. Meanwhile, the power consumption is high, so that the requirements for batteries to provide power by many portable devices cannot be met.
Generally speaking, the back light modules are divided into direct type back light modules and side type back light modules. Compared with the side type back light module, the direct type back light module is capable of providing high brightness, so that when the brightness requirement for the light source is high or being applied to a largely sized display device, the direct type back light module is commonly adopted. Furthermore, the direct type LED back light module uses the local dimming technology, and thus being more power saving, and meeting the environmental protection requirements; however, in order to eliminate the hot spot effect, the distance between the light source and the film sheet needs to be increased so as to provide an adequate light mixing distance, and as a result, the thickness of the back light module is increased, which is not of benefit to the demand of lightening and thinning of the displays.
Accordingly, the inventors of the present invention, through extensive researches and repeated experiments, invented an optical film composite including a light diffusion element having high diffusion properties and a brightness enhancement element. The optical film composite of the present invention is applicable to a direct type LED back light module of a large size display without increasing the light mixing distance, achieves the light uniformization effect, has the advantages of simple process, high yield, and ease of use, and can solve the problems existing in the art.